Over the air measurement module

ABSTRACT

An over the air measurement module comprises an antenna, adapted to receive a first measuring signal from a device under test or to transmit a second measuring signal to the device under test. It also comprises an analog signal processor, directly connected to said antenna, adapted to reduce a frequency of the received first measuring signal, resulting in a frequency reduced first measuring signal, or adapted to increase a frequency of a frequency reduced second measuring signal, resulting in the second measuring signal. It also has a connector connected to said analog signal processor and is adapted to output the first frequency reduced measuring signal or is adapted to receive the second frequency reduced measuring signal.

PRIORITY

This application claims priority of European patent application EP 16153 360.9 filed on Jan. 29, 2016 which is incorporated by referenceherewith.

FIELD OF THE INVENTION

The invention relates to an over the air measurement module formeasuring high frequency signals, especially communication signals overthe air.

BACKGROUND OF THE INVENTION

During recent years, radio frequencies employed for performingcommunication tasks have continually risen. Especially with frequenciesexceeding many GHz, new problems regarding the measurement of respectivesignals arise. By connecting the signal source to a measuring deviceusing a cable connection, the behavior of the device under test isinfluenced.

For example the document US 2015/0035707 A1 shows a slot line antenna ona printed circuit board. The antenna shown there is capable of receivinghigh frequency signals.

There arises the need of providing measuring means for measuring highfrequency signals with a high accuracy and a small size and hardwareeffort.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, an over the airmeasurement module is provided. The over the air measurement modulecomprises an antenna, which is adapted to receive a first measuringsignal from a device under test. Moreover, it comprises an analog signalprocessor which is directly connected to said the antenna and is adaptedto reduce a frequency of the received first measuring signal, resultingin a frequency reduced first measuring signal. Furthermore, the over theair measurement module comprises a connector, connected to said analogsignal processor, which is adapted to output the first frequency reducedmeasuring signal. It is thereby possible to acquire a measuring signalof an extremely high frequency without altering it and to provide alower frequency measuring signal to further measuring devices.

Alternatively or additionally, the connector is adapted to receive asecond frequency reduced measuring signal and provide it to the analogsignal processor which is then adapted to increase a frequency of thefrequency reduced second measuring signal, resulting in a secondmeasuring signal. The antenna is then adapted to transmit this secondmeasuring signal to the device under test. It is thereby possible toprovide a measuring signal of extremely high frequency to the deviceunder test in a controlled manner without influencing the measuringresults.

According to a preferred implementation form of the first aspect, theantenna is a planar antenna. A main radiation direction of the antennais in the plane of the planar antenna. It is thereby possible to achievea very low size of the over the air measurement module.

According to a further preferred development of this implementationform, at least some surfaces, advantageously all surfaces of themeasuring module facing in the main radiation direction of the antennaare adapted to absorb electromagnetic radiation and do not reflectelectromagnetic radiation. Thereby, reflections towards the device undertest are prevented. This increases the measuring accuracy.

According to a further preferred implementation form, at least somesurfaces, advantageously all surfaces of the measuring device facing inthe main radiation direction of the antenna are coated with a paintabsorbing electromagnetic radiation and/or covered with absorbermaterial absorbing electromagnetic radiation and/or fabricated fromabsorber material absorbing electromagnetic radiation. It is therebypossible to further reduce reflections towards the device under testthereby increasing the measuring accuracy.

According to a further preferred implementation form of the firstaspect, at least 50% of all surfaces preferably at least 80% of allsurfaces, most preferably all surfaces of the over the air measurementmodule facing the main radiation direction of the antenna are angledaway from a normal of the main radiation direction of the antenna by atleast 30°, preferably by at least 45°, most preferably by at least 60°.This further helps to reduce reflections towards the device under test,further increasing measuring accuracy.

According to a further preferred implementation form of the firstaspect, the over the air measurement module is tapered towards the mainradiation direction of the antenna. First of all, this measure alsoreduces reflections towards the device under test, thereby increasingmeasuring accuracy. Also, this measure allows for an especially smallfoot print of the over the air measurement module. This increases theflexibility of use.

According to a further preferred implementation form of the first aspectof the invention, if the antenna is adapted to receive the firstmeasuring signal from the device under test, the analog signal processoris adapted to reduce the frequency of the received first measuringsignal and the connector is adapted to output the first frequencyreduced measuring signal, and the analog signal processor comprises amixer, adapted to down-convert the first measuring signal to thefrequency reduced first measuring signal. It is thereby possible to useregular measuring devices for measuring the frequency reduced firstmeasuring signal without influencing the measuring result.

According to a further preferred development of the previousimplementation form, the analog signal processor further comprises afilter, adapted to perform a filtering of the first measuring signaland/or of the first frequency reduced measuring signal. Alternatively oradditionally, the analog signal processor comprises a power sensor,adapted to measure the power of the first frequency reduced measuringsignal. Alternatively or additionally, the analog signal processorcomprises an amplifier, adapted to amplify the first measuring signaland/or the first frequency reduced measuring signal. Additionally oralternatively, the analog signal processor furthermore comprises a radiofrequency switch, adapted to switch between different operating modes ofthe over the air measurement module. It is thereby possible to flexiblyperform a post processing of the first measuring signal and signalsderived therefrom.

According to a further preferred implementation form of the firstaspect, if the connector is adapted to receive the second frequencyreduced measuring signal, and the analog signal processor is adapted toincrease the frequency of the frequency reduced second measuring signal,and the antenna is adapted to transmit the second measuring signal tothe device under test, and the analog signal processor comprises amixer, adapted to up-convert the frequency reduced second measuringsignal to the second measuring signal. It is thereby possible togenerate the frequency reduced second measuring signal by for example aregular signal generator and to provide the second measuring signal ofan extremely high frequency to the device under test.

According to a further preferred development of the previousimplementation form, the analog signal processor further comprises afilter, adapted to perform a filtering of the second measuring signaland/or the second frequency reduced measuring signal. Alternatively oradditionally, the analog signal processor comprises an amplifier,adapted to amplify the second measuring signal and/or the secondfrequency reduced measuring signal. Moreover, alternatively oradditionally, the analog signal processor comprises a radio frequencyswitch, adapted to switch between different operating modes of the overthe air measurement module. It is thereby possible to flexibly perform apre-processing of the second measuring signal before handing it to thedevice under test.

According to a further preferred implementation form of the firstaspect, the over the air measurement module comprises a substrate,advantageously a printed circuit board. The antenna and the analogsignal processor are arranged on the substrate. The antenna is planarwith the substrate. The main radiation direction of the antenna istowards an edge of the substrate. It is thereby possible to achieve anextremely small size and low footprint of the over the air measurementmodule.

According to a further preferred development of the previousimplementation form, the substrate has a relative permittivity ε_(r) ofε_(r)<4, preferably ε_(r)<2, most preferably ε_(r)<1.5. Additionally oralternatively, the substrate has a relative permeability μ_(r) ofμ_(r)<3, preferably μ_(r)<2, most preferably μ_(r)<1.5. A very lowinfluence of the substrate on the measuring signal is thereby achieved.

According to a further preferred development of the previous twoimplementation forms, the antenna is a tapered slot line antenna,advantageously a Vivaldi antenna. It is thereby possible, to achievesatisfactory high frequency characteristics, while achieving a verysmall size of the antenna.

According to a further preferred development form of the previousimplementation form, the substrate comprises an opening betweenconductors of the tapered slot line antenna. Additionally oralternatively, a substrate bridge connects opposite parts of the taperedslot line antenna in an area of an antenna aperture. A very stableconstruction of the antenna with beneficial radio frequencycharacteristics is thereby achieved.

According to a second aspect of the invention, a measuring systemcomprising a previously described over the air measurement module isprovided. The measuring system comprises a measuring device. Themeasuring device is adapted to receive and measure the frequency reducedfirst measuring signal from the over the air measurement module.Alternatively or additionally, the measuring device is adapted toprovide the frequency reduced second measuring signal to the over theair measurement module. A very flexible and accurate measurement isthereby possible.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are now further explained withrespect to the drawings, by way of example only. The invention is,however, not limited to these embodiments. In the drawings:

FIG. 1 shows a system with a first embodiment of the over the airmeasurement module and a measuring device of the invention in a top-downview;

FIG. 2 shows the first embodiment of the over the air measurement moduleof the invention in a side-view;

FIG. 3 shows a second embodiment of the over the air measurement moduleof the invention in a three-dimensional view; and

FIG. 4 shows the second embodiment of the over the air measurementmodule of the invention in a cut-view.

DETAILED DESCRIPTION OF THE DRAWINGS

First we demonstrate the general construction and function of an overthe air measurement module along FIG. 1 and FIG. 2. Along FIG. 3 andFIG. 4 further details of another implementation form are described.Similar entities and reference numbers in different figures have beenpartially omitted.

In FIG. 1, a first embodiment of the over the air measurement module 1according to the first aspect of the invention is shown. The over theair measurement module 1 comprises a housing 15 which contains asubstrate 18, advantageously a printed circuit board. On the substrate18, two antenna elements 16, 17 forming a tapered slot line antenna 19,are arranged. The antenna 19 is connected to an analog signal processor14 which is also arranged on the substrate 18. The analog signalprocessor moreover is connected to a connector 13 which serves as aninterface 13. Connectable to the interface 13 is a measuring device 2,which is not part of the over the air measurement module 1. The antenna19 has a main radiation direction towards the right edge of thesubstrate 18, indicated by an arrow in the figures. A device under test3 is suitably arranged in this direction.

In order to minimize reflections from the over the air measurementmodule 1, the housing 15 is tapered towards the main radiation directionof the antenna 19. This tapering reduces the effective surface area,which can produce reflections. In order to further reduce suchreflections, the housing 15 can be fabricated from an electromagneticradiation absorbing material. It can also be covered with such amaterial or can be coated with an absorptive paint. The housing 15furthermore comprises a back plate 11, which is covered with absorptivematerial 12 in order to further reduce reflections.

The over the air measurement module 1 is suitable for two types ofmeasurements. In a first type of measurement, a first measuring signalemitted from the device under test 3 is received by the antenna 19 andhanded to the analog signal processor 14. The analog signal processor 14reduces the frequency of the first measuring signal resulting in afrequency reduced first measuring signal. This is for example done bydown-converting the first measuring signal using a mixer. Additionally,the analog signal processor in this case can comprise one or morefilters for filtering the first measuring signal or the frequencyreduced first measuring signal, a power sensor, which can be used fordirectly measuring a power of the frequency reduced first measuringsignal, an amplifier for amplifying the first measuring signal or thefirst frequency reduced measuring signal, and a radio frequency switchfor switching between the previously described measuring option and themeasuring option described in the following. The processed frequencyreduced measuring signal is then handed on to the connector 13, whichpasses on the signal to for example an external measuring device 2 forfurther processing the frequency reduced measuring signal.

Alternatively, the over the air measurement module can be used foranother type of measurement. In this case, the connector 13 receives afrequency reduced second measuring signal from the measuring device 2.It is handed on to the analog signal processor 14. The analog signalprocessor 14 increases the frequency of the frequency reduced secondmeasuring signal resulting in a second measuring signal. This is forexample done by mixing the frequency reduced second measuring signalwith a further local oscillator signal. The second measuring signal isthen transmitted by the antenna 19 to the device under test 3. Also, inthis case, the analog signal processor can comprise additionalcomponents. The analog signal processor can comprise a filter, forfiltering the second measuring signal and/or the second frequencyreduced measuring signal. Also, the analog signal processor can comprisean amplifier for amplifying the second measuring signal and/or thesecond frequency reduced measuring signal. Moreover, the analog signalprocessor can comprise a radio frequency switch, adapted to switchbetween different operating modes of the over the air measurementmodule.

Also here, the measurement system 30 according to the second aspect ofthe invention is depicted. The measuring system 30 comprises the overthe air measurement module 1 and the measuring device 2. The measuringdevice 2 is adapted to receive and measure the frequency reduced firstmeasuring signal and/or to provide the frequency reduced secondmeasuring signal to be transmitted to the device under test 3 as secondmeasuring signal.

In FIG. 2 the over the air measurement module of FIG. 1 is shown in acut view from the side. Here it can be seen that the analog signalprocessor 14 and the connector 13 are arranged on the substrate 18.Moreover, the tapering of the housing 15 and the arrangement of theabsorbers 12 can be seen.

In FIG. 3 a second embodiment of the over the air measurement module 1is shown. Here, a three-dimensional view of the over the air measurementmodule 1 is depicted. The housing 15 comprises a first part 15 a and asecond part 15 b. The two housing parts surround the substrate 18 andhold the substrate 18 between themselves. The substrate 18 comprises anopening 27 between the antenna elements 16 and 17. This opening 27further reduces the influence of the substrate material on the receivedor transmitted signal. For reasons of stability, the embodiment shownhere comprises a substrate bridge 28 connecting opposite parts of thetapered slot line antenna in the area of the antenna aperture.

Moreover, the over the air measurement module 1 comprises an absorber20, which is arranged surrounding the substrate 18 at the narrow end ofthe tapered slot line antenna 19. The absorber 20 prevents reflectionstowards the device under test 2.

Moreover, in this embodiment, the geometric shape of the over the airmeasurement module 1 is evident. Especially, it is evident here, thatthe over the air measurement module 1 is tapered towards the mainradiation direction of the antenna 19. Moreover, it is evident that allsurfaces of the over the air measurement module 1 facing the mainradiation direction of the antenna 19 are angled away from a normal ofthe main radiation direction of the antenna 19. This leads to anespecially low reflectivity for signals emitted by the device under test2. Here, only the very small surfaces 23, 24 point towards the deviceunder test. All other surfaces 21, 22, 25, 26 are angled away from thedevice under test.

Especially, at least 50%, preferably at least 80%, most preferably allsurfaces of the over the air measurement module facing the mainradiation direction of the antenna are therefore angled away from anormal of the main radiation direction of the antenna by at least 30°,preferably by at least 45°, most preferably by at least 60°.

In order to further reduce the effect of the substrate 18 on thereceived or transmitted signal, the relative permittivity ε_(r) is low.Especially, it is lower than 4, preferably ε_(r)<2, most preferablyε_(r)<1.5. For the same reason, the relative permeability μ_(r) is low.Advantageously it is below 3, preferably μ_(r)<2, most preferablyμ_(r)<1.5.

In FIG. 4 a cut open view of the embodiment of FIG. 3 is shown. Here itis evident that the housing 15 comprises an opening 29, which enclosesthe substrate 18. Arranged on the substrate 18 is the analog signalprocessor 14, which is connected to the antenna element 16, 17 of theantenna 19. As explained earlier, the analog signal processor 14processes signals received by the antenna 19 and signals to betransmitted by the antenna 19. Especially the analog signal processor 14performs a frequency conversion.

Evident from FIG. 4 is that the absorber 20 surrounds the substrate 18on both sides in order to reduce the reflections towards the deviceunder test.

Instead of forming the antenna 19 as depicted here, it is also possibleto use two tapered slot line antennas on substrates, which are arrangedorthogonally. In this case, a dual linear polarization measurement canbe provided. The signals of these two antennas can be handled separatelyor can be combined.

Also advantageously, a power sensor can be integrated into the analogsignal processor 14. A power measurement of signals received from thedevice under test can then be performed there. The power measurement inthis case would be performed under a frequency reduced first measuringsignal. In this case, a load resistor of the power sensor of the antennahas a higher value than 50 Ohm.

As a power sensor, a diode sensor produced in slot line technology canbe used.

In addition, a rectification and/or a bandwidth limitation and/or ananalog-digital-conversion can also be integrated into the analog signalprocessor. The analog signal processor 14 can moreover be adapted toprovide an intermediate frequency signal or a baseband signal to theconnector 13.

Advantageously, the over the air measurement module 1 is adapted toperform a wireless measurement. This means that the connector 13 can beimplemented as a wireless interface for wirelessly transmitting themeasuring results to the measuring device 2.

Especially, it is possible to split the measuring system 30 into anantenna module and a detector module. The antenna module would thencomprise all aspects presently contained in the over the air measurementmodule, while the detector module would comprise at least a detector fordetermining certain aspects of the measured signal, for example thepower of the signal. Moreover, a sensor/processing module could beseparately constructed. In this case, the over the air measurementmodule 1 could be split into an antenna module only comprising theantenna 19 and a processing module comprising the analog signalprocessor 14. The antenna module, processing module and detector modulecan be integrated into a single module or housing. Also they can beseparately constructed. Especially, an integration of the detectormodule and the antenna module is possible.

In order to connect the different modules, especially the sensor module,the antenna module, the detector module and the processing module,electrical conductors, for example coplanar transmission lines can beused. Also the use of optical transmission lines is possible.

In order to minimize noise, a chopper can be integrated into thedetector module. By repeatedly reversing the polarity of the measuredsignal, the influence of noise can be mitigated. Especially, theinfluence of accidently coupling noise signals can be reduced.

Advantageously, the detector can be formed based on a coplanartransmission line. This allows for an easy transmission of the detectedpower to further components.

Advantageously, the antenna signals, especially if the antenna is a slotline antenna, can be converted to a signal on a coplanar transmissionline so that they can be more easily handled on the circuit board andsupplied to the further components.

The change of the transmission typology from slot line to coplanar canbe performed either between the antenna and the analog signal processoror between the analog signal processor and the connector.

The invention is not limited to the examples and especially not to aspecific measurement direction. Also the measured signals are notlimited to a specific communications task. The characteristics of theexemplary embodiments can be used and can be combined in anyadvantageous combination.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Numerous changes to the disclosedembodiments can be made in accordance with the disclosure herein withoutdeparting from the spirit or scope of the invention. Thus, the breadthand scope of the present invention should not be limited by any of theabove described embodiments. Rather, the scope of the invention shouldbe defined in accordance with the following claims and theirequivalents.

Although the invention has been illustrated and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art upon the reading andunderstanding of this specification and the annexed drawings. Inaddition, while a particular feature of the invention may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application.

What is claimed is:
 1. An over the air measurement module, comprising:an antenna, adapted to receive a first measuring signal from a deviceunder test or adapted to transmit a second measuring signal to thedevice under test, an analog signal processor, directly connected tosaid antenna, adapted to reduce a frequency of the received firstmeasuring signal, resulting in a frequency reduced first measuringsignal, or adapted to increase a frequency of a frequency reduced secondmeasuring signal, resulting in the second measuring signal, and aconnector, connected to said analog signal processor, adapted to outputthe first frequency reduced measuring signal, or adapted to receive thesecond frequency reduced measuring signal, wherein the antenna is aplanar antenna, and wherein a main radiation direction of the antenna isin the plane of the planar antenna, wherein at least some surfaces, ofthe over the air measuring module facing in the main radiation directionof the antenna are adapted to absorb electromagnetic radiation and notreflect electromagnetic radiation, and wherein at least 50% of surfacesof the over the air measurement module facing the main radiationdirection of the antenna are angled away from a normal of the mainradiation direction of the antenna by at least 30°.
 2. The over the airmeasurement module according to claim 1, wherein at least some surfacesof the over the air measuring module facing in the main radiationdirection of the antenna are coated with a paint absorbingelectromagnetic radiation or covered with absorber material absorbingelectromagnetic radiation or fabricated from absorber material absorbingelectromagnetic radiation.
 3. The over the air measurement moduleaccording to claim 1, wherein over the air measurement module is taperedtowards the main radiation direction of the antenna.
 4. The over the airmeasurement module according to claim 1, wherein, if the antenna isadapted to receive the first measuring signal from the device undertest, the analog signal processor is adapted to reduce the frequency ofthe received first measuring signal, and the connector is adapted tooutput the first frequency reduced measuring signal, and the analogsignal processor comprises a mixer, adapted to down convert the firstmeasuring signal to the frequency reduced first measuring signal.
 5. Theover the air measurement module according to claim 4, wherein the analogsignal processor further comprises: a filter, adapted to perform afiltering of the first measuring signal or of the first frequencyreduced measuring signal, or a power sensor, adapted to measure thepower of the first frequency reduced measuring signal, or an amplifier,adapted to amplify the first measuring signal or the first frequencyreduced measuring signal, or a radio frequency switch, adapted to switchbetween different operating modes of the over the air measurementmodule.
 6. The over the air measurement module according to claim 1,wherein, if the connector is adapted to receive the second frequencyreduced measuring signal, the analog signal processor is adapted toincrease the frequency of the frequency reduced second measuring signal,the antenna is adapted to transmit the second measuring signal to thedevice under test, and the analog signal processor comprises a mixer,adapted to up convert the frequency reduced second measuring signal tothe second measuring signal.
 7. The over the air measurement moduleaccording to claim 6, wherein the analog signal processor furthercomprises: a filter, adapted to perform a filtering of the secondmeasuring signal or the second frequency reduced measuring signal, or anamplifier, adapted to amplify the second measuring signal or the secondfrequency reduced measuring signal, or a radio frequency switch, adaptedto switch between different operating modes of the over the airmeasurement module.
 8. The over the air measurement module according toclaim 1, wherein over the air measurement module comprises a substrate,advantageously a printed circuit board, wherein the antenna and theanalog signal processor are arranged on the substrate, wherein theantenna is planar with the substrate, and wherein the main radiationdirection of the antenna is towards an edge of the substrate.
 9. Theover the air measurement module according to claim 8, wherein thesubstrate has a relative permittivity ε_(r) of ε_(r)<4, preferablyε_(r)<2, most preferably ε_(r)<1.5 or wherein the substrate has arelative permeability μ_(r) of μ_(r)<3, preferably μ_(r)<2, mostpreferably μ_(r)<1.5.
 10. The over the air measurement module accordingto claim 8, wherein the antenna is a tapered slotline antenna,preferably a Vivaldi antenna.
 11. The over the air measurement moduleaccording to claim 10, wherein the substrate comprises an openingbetween conductors of the tapered slotline antenna, or wherein asubstrate bridge connects opposite parts of the tapered slotline antennain an area of an antenna aperture.
 12. Measuring system comprising anover the air measurement module according to claim 1 and a measuringdevice, wherein the measuring device is adapted to receive and measurethe frequency reduced first measuring signal from the over the airmeasurement module or is adapted to provide the frequency reduced secondmeasuring signal to the over the air measurement module.